Control system for work vehicle, control method, and work vehicle

ABSTRACT

A current terrain acquisition device acquires current terrain information indicating the current terrain to be worked. A controller is configured to decide a virtual design surface that is located below the current terrain and has an inclination angle. The controller is configured to generate a command signal to the work implement of the work vehicle to move the work implement along the virtual design surface. The controller is configured to update the current terrain information with the current terrain acquisition device as the movement proceeds, and change the inclination angle with the updated current terrain information.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Japanese Patent Application No.2016-152264 filed on Aug. 2, 2016, the disclosure of which is herebyincorporated herein by reference in its entirety.

TECHNICAL FIELD

The present invention relates to a control system for a work vehicle, toa control method, and to a work vehicle.

BACKGROUND

A control system has been proposed in the past in which the position ofa work implement is automatically adjusted in a work vehicle such as abulldozer or a grader. For example, Japanese Patent No. 5,247,939discloses digging control and grading control. In digging control, theposition of the blade is automatically adjusted so that the load on theblade will match a target load. In grading control, the position of theblade is automatically adjusted so that the cutting edge of the blademoves along a design terrain indicating the target shape to be dug.

SUMMARY

With the above-mentioned conventional control system, the occurrence ofshoe slip can be minimized by raising the work implement when the loadon the work implement becomes excessive. This allows the work to beperformed more efficiently.

With a conventional control system, however, as shown in FIG. 15, firstthe work implement is controlled so as to follow the design terrain 100by grading control. If the load on the work implement subsequentlyincreases, the work implement is raised by load control (see thetrajectory 200 of the work implement in FIG. 15). Therefore, whendigging a terrain 300 with large undulations, the load exerted on thework implement may increase rapidly, causing the work implement to risesuddenly. If that happens, a very uneven terrain will be formed, makingit difficult to perform digging work smoothly. Also, there is the riskthat the terrain being dug will be prone to becoming rough and thefinish quality will suffer.

It is an object of the present invention to provide a control system fora work vehicle, a control method, and a work vehicle, with which diggingwork can be performed efficiently and with good finish quality.

The control system according to a first aspect is a work vehicle controlsystem that includes a current terrain acquisition device and acontroller. The current terrain acquisition device acquires currentterrain information indicating the current terrain to be worked. Thecontroller is configured to decide a virtual design surface that islocated below the current terrain and has an inclination angle. Thecontroller is configured to generate a command signal to a workimplement of the work vehicle to move the work implement along thevirtual design surface. The controller is configured to update thecurrent terrain information with the current terrain acquisition deviceas movement proceeds, and modify the inclination angle according to theupdated current terrain information.

The method for controlling a work vehicle according to a second aspectincludes the following steps. In the first step, current terraininformation indicating the current terrain to be worked is acquired. Inthe second step, an inclined virtual design surface located below thecurrent terrain is decided. In the third step, a command signal isgenerated to the work implement of the work vehicle to move the workimplement along the virtual design surface. The virtual design surfaceis decided so that the inclination angle gradually decreases, byrepeatedly updating the current terrain and deciding the virtual designsurface.

The work vehicle according to a third aspect includes a work implementand a controller. The controller is configured to decide an inclinedvirtual design surface that is located below the current terrain to beworked. The controller is configured to move the work implement alongthe virtual design surface. The controller is configured to decide thevirtual design surface so that the inclination angle graduallydecreases, by repeatedly updating the current terrain and deciding thevirtual design surface.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a work vehicle according to an embodiment;

FIG. 2 is a block diagram of the configuration of the drive system andcontrol system of the work vehicle;

FIG. 3 is a simplified diagram of the configuration of the work vehicle;

FIG. 4 is a flowchart of the processing involved in automatic control ofa work implement in digging work;

FIG. 5 is a diagram showing an example of the final design terrain andthe current terrain;

FIG. 6 is a diagram showing a method for calculating the inclinationangle of the virtual design surface;

FIG. 7 is a diagram showing a method for calculating the estimated dugsoil volume;

FIG. 8 is a diagram showing a method for calculating the current heldsoil volume;

FIG. 9 is a flowchart showing the processing involved in automaticcontrol of the work implement in digging work;

FIG. 10 is a diagram showing an example of a virtual design surface indigging work;

FIG. 11 is a diagram showing an example of a virtual design surface inearthmoving work;

FIGS. 12A, 12B and 12C are diagrams showing an example of work done by awork vehicle on an upward slope;

FIGS. 13A, 13B and 13C are diagrams showing an example of work done by awork vehicle on an upward slope;

FIGS. 14A, 14B and 14C are diagrams showing an example of work done by awork vehicle on a downward slope; and

FIG. 15 is a diagram showing digging work according to prior art.

DETAILED DESCRIPTION

The work vehicle according to an embodiment will now be describedthrough reference to the drawings. FIG. 1 is a side view of a workvehicle 1 according to an embodiment. The work vehicle 1 according tothis embodiment is a bulldozer. The work vehicle 1 includes a vehiclebody 11, a drive unit 12, and a work implement 13.

The vehicle body 11 includes a cab 14 and an engine compartment 15. Adriver's seat (not shown) is disposed in the cab 14. The enginecompartment 15 is disposed in front of the cab 14. The drive unit 12 isattached to a lower portion of the vehicle body 11. The drive unit 12includes a pair of right and left crawler belts 16. Only the leftcrawler belt 16 is shown in FIG. 1. Rotation of the crawler belts 16propels the work vehicle 1. The travel of the work vehicle 1 may beeither autonomous travel, semi-autonomous travel, or travel underoperation by the operator.

The work implement 13 is attached to the vehicle body 11. The workimplement 13 includes a lift frame 17, a blade 18, a lift cylinder 19,an angle cylinder 20, and a tilt cylinder 21.

The lift frame 17 is attached to the vehicle body 11 so as to be movableup and down around an axis X extending in the vehicle width direction.The lift frame 17 supports the blade 18. The blade 18 is disposed infront of the vehicle body 11. The blade 18 moves up and down as the liftframe 17 moves up and down.

The lift cylinder 19 is linked to the vehicle body 11 and the lift frame17. As the lift cylinder 19 expands and contracts, the lift frame 17rotates up and down around the axis X.

The angle cylinder 20 is linked to the lift frame 17 and the blade 18.As the angle cylinder 20 telescopes in and out, the blade 18 rotatesaround the axis Y extending in the approximate up and down direction.

The tilt cylinder 21 is linked to the lift frame 17 and the blade 18. Asthe tilt cylinder 21 expands and contracts, the blade 18 rotates aroundthe axis Z extending in the approximate longitudinal direction of thevehicle.

FIG. 2 is a block diagram of the configuration of the drive system 2 andthe control system 3 of the work vehicle 1. As shown in FIG. 2, thedrive system 2 includes an engine 22, a hydraulic pump 23, and a powertransmission device 24.

The hydraulic pump 23 is driven by the engine 22 and dischargeshydraulic fluid. The hydraulic fluid discharged from the hydraulic pump23 is supplied to the lift cylinder 19, the angle cylinder 20, and thetilt cylinder 21. In FIG. 2, just one hydraulic pump 23 is shown, but aplurality of hydraulic pumps may be provided.

The power transmission device 24 transmits the drive force of the engine22 to the drive unit 12. The power transmission device 24 may be, forexample, a hydro-static transmission (HST). Alternatively, the powertransmission device 24 may be, for example, a torque converter or atransmission having a plurality of gears.

The control system 3 includes an operating device 25, a controller 26,and a control valve 27. The operating device 25 is used to operate thework implement 13 and the drive unit 12. The operating device 25 isdisposed in the cab 14. The operating device 25 receives operator inputsfor driving the work implement 13 and the drive unit 12, and outputs anoperation signal corresponding to the input. The operating device 25includes, for example, a control lever, a pedal, a switch, or the like.

For example, the operating device 25 for the drive unit 12 is providedto allow for operation in a forward position, a reverse position, and aneutral position. When the operation position of the operating device 25is the forward position, the drive unit 12 or the power transmissiondevice 24 is controlled so that the work vehicle 1 moves forward. Whenthe operation position of the operating device 25 is the reverseposition, the drive unit 12 or the power transmission device 24 iscontrolled so that the work vehicle 1 reverses.

The controller 26 is programmed to control the work vehicle 1 on thebasis of acquired information. The controller 26 includes a processorsuch as a CPU, for example. The controller 26 acquires an operationsignal from the operating device 25. The controller 26 controls thecontrol valve 27 on the basis of the operation signal. The controller 26is not limited to a single unit, and may be divided up into a pluralityof controllers.

The control valve 27 is a proportional control valve and is controlledby a command signal from the controller 26. The control valve 27 isdisposed between the hydraulic pump 23 and hydraulic actuators such asthe lift cylinder 19, the angle cylinder 20, and the tilt cylinder 21.The control valve 27 controls the flow of hydraulic fluid supplied fromthe hydraulic pump 23 to the lift cylinder 19, the angle cylinder 20,and the tilt cylinder 21. The controller 26 generates a command signalto the control valve 27 so that the work implement 13 operates inaccordance with the operation of the operating device 25 discussedabove. Consequently, the lift cylinder 19, the angle cylinder 20, andthe tilt cylinder 21 are controlled according to the operation amount ofthe operating device 25. The control valve 27 may be a pressureproportional control valve. Alternatively, the control valve 27 may bean electromagnetic proportional control valve.

The control system 3 includes a lift cylinder sensor 29. The liftcylinder sensor 29 senses the stroke length of the lift cylinder 19(hereinafter referred to as “lift cylinder length L”). As shown in FIG.3, the controller 26 calculates the lift angle θlift of the blade 18 onthe basis of the lift cylinder length L. FIG. 3 is a simplified diagramof the configuration of the work vehicle 1.

In FIG. 3, the origin position of the work implement 13 is indicated bya two-dot chain line. The origin position of the work implement 13 isthe position of the blade 18 in a state in which the cutting edge of theblade 18 is in contact with the ground on a horizontal surface. The liftangle θlift is the angle from the origin position of the work implement13.

As shown in FIG. 2, the control system 3 includes a position sensingdevice 31. The position sensing device 31 measures the position of thework vehicle 1. The position sensing device 31 is the main body of acurrent terrain acquisition device (discussed below). The positionsensing device 31 includes a GNSS (global navigation satellite system)receiver 32 and an IMU 33. The GNSS receiver 32 is, for example, a GPS(global positioning system) receiver and an antenna. The antenna of theGNSS receiver 32 is disposed on the cab 14. The GNSS receiver 32receives positioning signals from a satellite and calculates theposition of the antenna based on the positioning signal to generatevehicle position information. The GNSS receiver 32 sends the controller26 a vehicle position signal indicating the position of the work vehicle1. The controller 26 acquires vehicle position information from the GNSSreceiver 32.

The IMU 33 is an inertial measurement unit. The IMU 33 acquires vehicleinclination angle information and vehicle acceleration information. Thevehicle inclination angle information indicates the angle of the vehiclelongitudinal direction with respect to the horizontal (pitch angle), andthe angle of the vehicle lateral direction with respect to thehorizontal (roll angle). The vehicle acceleration information indicatestravel direction information about the work vehicle 1. The IMU 33 sendsthe controller 26 a vehicle inclination angle signal indicating theattitude of the work vehicle 1, and a vehicle acceleration signalindicating the travel direction. The controller 26 acquires vehicleinclination angle information and vehicle acceleration information fromthe IMU 33.

The controller 26 calculates a cutting edge position P0 from the liftcylinder length L, the vehicle position information, and the vehicleinclination angle information. As shown in FIG. 3, the controller 26calculates the global coordinates of the GNSS receiver 32 based on thevehicle position information. The controller 26 calculates the liftangle θlift based on the lift cylinder length L. The controller 26calculates the local coordinates of the cutting edge position P0 withrespect to the GNSS receiver 32 based on the lift angle θlift andvehicle size information. The controller 26 calculates the traveldirection of the work vehicle 1 from the vehicle accelerationinformation. The vehicle size information is stored in the storagedevice 28 and indicates the position of the work implement 13 withrespect to the GNSS receiver 32. The controller 26 calculates the globalcoordinates of the cutting edge position P0 based on the globalcoordinates of the GNSS receiver 32, the local coordinates of thecutting edge position P0, and the vehicle inclination angle information.The controller 26 acquires the global coordinates of the cutting edgeposition P0 as cutting edge position information.

The control system 3 includes a storage device 28. The storage device 28includes, for example, a memory and an auxiliary storage device. Thestorage device 28 may be, for example, a RAM, a ROM, or the like. Thestorage device 28 may be a semiconductor memory, a hard disk, or thelike.

The storage device 28 stores design terrain information and work siteterrain information. The design terrain information indicates theposition and shape of the final design terrain. The final design terrainis the target terrain to be worked at the work site. The design terraininformation is, for example, a construction drawing in athree-dimensional data format. The work site terrain information is thecurrent terrain information for the work site around the work vehicle 1.The work site terrain information is, for example, a currenttopographical survey in a three-dimensional data format, which can beobtained by aerial laser survey. The controller 26 acquires the currentterrain information. The current terrain information indicates theposition and shape of the current terrain to be worked at the work site.The current terrain to be worked is the terrain of the region along thetravel direction of the work vehicle 1. The current terrain informationis acquired by calculation in the controller 26 from the work siteterrain information and the position and travel direction of the workvehicle 1 obtained from the above-mentioned position sensing device 31.The controller 26 automatically controls the work implement 13 on thebasis of the current terrain information, the design terraininformation, and the cutting edge position information.

The automatic control of the work implement 13 may be semi-automaticcontrol performed together with manual operation by the operator.Alternatively, the automatic control of the work implement 13 may befully automatic control performed without any manual operation by anoperator.

The automatic control of the work implement 13 in digging work executedby the controller 26 will now be described. FIG. 4 is a flowchart of theprocessing involved in automatic control of the work implement 13 indigging work.

As shown in FIG. 4, in step S101, the controller 26 acquires currentposition information. Here, the controller 26 acquires the currentcutting edge position P0 of the work implement 13 as discussed above.

In step S102, the controller 26 acquires design terrain information. Asshown in FIG. 5, the design terrain information includes the heightZ_(design) of the final design terrain 60 at a plurality of points atpredetermined intervals in the travel direction of the work vehicle 1.In FIG. 5, the final designed terrain 60 has a flat shape parallel tothe horizontal direction, but it may have a different shape.

In step S103, the controller 26 acquires the current terraininformation. The controller 26 acquires the current terrain informationby calculation from the work site terrain information obtained from thestorage device 28, and the vehicle position information and the traveldirection information obtained from the position sensing device 31. Thecurrent terrain acquisition device includes the position sensing device31 and the controller 26. The current terrain information is informationabout the terrain located in the travel direction of the work vehicle 1.FIG. 5 is a cross section of the current terrain 50. In FIG. 5, thevertical axis is the height of the terrain, and the horizontal axis isthe distance from the current position in the travel direction of thework vehicle 1.

More precisely, the current terrain information includes the heights Z0to Zn of the current terrain 50 at a plurality of points up to apredetermined terrain recognition distance do from the current positionin the travel direction of the work vehicle 1. In this embodiment, thecurrent position is a position determined on the basis of the currentcutting edge position P0 of the work vehicle 1. However, the currentposition may be determined on the basis of the current position ofanother part of the work vehicle 1. The plurality of points are arrangedat predetermined intervals, such as every meter.

The controller 26 acquires position information indicating the latesttrajectory of the cutting edge position P0 as work site terraininformation. The work site terrain information stored in the storagedevice 28 is updated with the acquired work site terrain information.Therefore, the position sensing device 31 functions as a terraininformation acquisition device that acquires the latest terraininformation.

Alternatively, the controller 26 may calculate the position of thebottom face of the crawler belt 16 from vehicle position information andvehicle size information, and acquire position information indicatingthe trajectory of the bottom face of the crawler belt 16 as work siteterrain information. In this case, the work terrain information can beupdated immediately. Alternatively, the work site terrain informationmay be generated from survey data measured by a surveying device outsidethe work vehicle 1. Aerial laser surveying may be used as an externalsurveying device, for example. In this case, the external surveyingdevice is a terrain information acquisition device. Alternatively, thecurrent terrain 50 may be photographed with a camera, and work siteterrain information may be generated from the image data obtained by thecamera. For example, aerial photographic surveying using a UAV (unmannedaerial vehicle) may be used. In this case, the image data processingsystem including the camera is a terrain information acquisition device.In the case of an external surveying device or a camera, the work siteterrain information is updated at predetermined intervals, or wheneverneeded.

In step S104, the soil volume of the current terrain 50 is calculated.Here, the controller 26 calculates the soil volume of the currentterrain 50 on the basis of the height of the current position. Thecontroller 26 calculates the soil volume S_(volume) of the currentterrain 50 from the following formula (1).

$\begin{matrix}{S_{volume} = {\sum\limits_{k = 1}^{n}{{\frac{Z_{k - 1} + Z_{k}}{2} - Z_{0}}}}} & {{Formula}\mspace{14mu} 1}\end{matrix}$

In this embodiment, the height of the current position is the height Z0of the current terrain 50 located in the vertical direction of thecurrent cutting edge position P0. However, the height of the currentposition may be different from the height Z0 of the current terrain 50located in the vertical direction of the current cutting edge positionP0. For example, the height of the current position may be the height ofthe current cutting edge position P0. Alternatively, the height of thecurrent position may be the height Z_(GL) of a perpendicular from thecurrent cutting edge position P0 to the plane that includes the bottomface of the crawler 16.

In calculating the soil volume, it is assumed that the cross sectionalarea of the current terrain 50 in the travel direction of the workvehicle 1 corresponds to the soil volume, and the size of the currentterrain 50 in the width direction of the work vehicle 1 is not takeninto account. However, the soil volume may be calculated by taking intoaccount the size of the current terrain 50 in the width direction of thework vehicle 1.

In step S105, it is determined whether or not a first starting conditionis satisfied. The first starting condition includes the followingconditions (1) and (2).

(1) The soil volume S_(volume) of the current terrain 50 is equal to orgreater than a predetermined undulation determination thresholdS_(const).

(2) The operating position of the operating device 25 is the forwardposition.

The controller 26 determines whether or not there are undulations in thecurrent terrain 50 according to the first starting condition. Meetingthe first starting condition means that the work vehicle 1 is movingforward and there is a terrain that can be worked in that forwarddirection. When the first starting condition is satisfied, the flowproceeds to step S106. When the first starting condition is notsatisfied, the flow returns to step S101. The processing from step S101to step S105 is repeated at predetermined intervals until the firststarting condition is satisfied.

In step S106, the inclination angle α of a virtual surface 70′ iscalculated. The virtual surface 70′ is a surface that substantiallyforms the virtual design surface when a predetermined condition issatisfied. The virtual design surface is a surface indicating thecutting edge target position of the work implement 13 during work by thework vehicle 1. The virtual design surface 70 includes a virtual surfaceinclined at an angle α. FIG. 6 illustrates the calculation of theinclination angle α. The virtual surface 70′ is assumed for calculationof the inclination angle α to be located below the simplified currentterrain 50S and inclined at an inclination angle α with respect to thehorizontal direction. The baseline extending horizontally in FIG. 6shows a horizontal plane 80 at the height of the current position of thework vehicle 1. For example, the horizontal plane 80 has the height ofthe cutting edge P0 of the work implement 13 of the work vehicle 1. Thevirtual surface 70′ is a straight line in a vertical plane including thetravel direction of the work vehicle 1. The virtual surface 70 in thevertical plane may be a curved line. The simplified current terrain 50Sis a terrain that approximates the current terrain 50 as a shelf shape.The simplified current terrain 50S includes a height L, an inclinationangle θ, and a base point BP. The controller 26 decides the inclinationangle α so that the soil volume of the simplified current terrain 50Slocated above the virtual surface 70′ will be a predetermined targetsoil volume S. As shown in FIG. 6, the controller 26 decides theinclination angle α of the virtual surface 70′ so that the crosssectional area of the simplified current terrain 50S located above thevirtual surface 70′ will be the target soil volume S.

More precisely, the controller 26 calculates the inclination angle αfrom the following formula (2).

$\begin{matrix}{\alpha = \frac{L^{2} \cdot \theta}{L^{2} + {2S{\theta }}}} & {{Formula}\mspace{14mu} 2}\end{matrix}$

L is the height of the undulations in the simplified current terrain50S. For example, L may be the difference between the maximum andminimum values for the heights Z0 to Zn at a plurality of points in theabove-mentioned current terrain 50. The target soil volume S may bedecided on the basis of the capacity of the blade, for example.

θ is the inclination angle of the simplified current terrain 50S. Thecontroller 26 decides the inclination angle θ of the simplified currentterrain 50S from the above-mentioned current terrain information.Specifically, the inclination angle θ is the maximum value of theinclination angle at a plurality of points in the current terrain 50.Alternatively, the inclination angle θ may be the average value of theinclination angle at a plurality of points in the current terrain 50.Here, the inclination angle is the angle formed by the horizontal plane80 and the extrapolation of a line segment connecting two points in thecurrent terrain 50. The point at which the extrapolation of the currentterrain having the maximum inclination angle (θ) intersects thehorizontal plane 80 is the base point BP. The virtual surface 70′ isassumed for the calculation of the inclination angle α to pass throughthe base point BP.

However, when the inclination angle α calculated from Formula 2 above isgreater than a predetermined upper limit value α_(max), the controller26 sets the upper limit value α_(max) as the inclination angle α. Theupper limit value α_(max) may be, for example, a value determined on thebasis of the maximum digging angle of which the work vehicle 1 iscapable.

Also, when the inclination angle α calculated from Formula 2 is lessthan a predetermined lower limit value α_(min), the controller 26 setsthe lower limit value α_(min) as the inclination angle α. The lowerlimit value α_(min) may be L/dn, for example, where dn is theabove-mentioned terrain recognition distance. That is, the lower limitvalue α_(min) may be the lower limit value of the inclination angle thatcan be attained by the virtual surface 70′ within the terrainrecognition distance dn from the current position to the top of thesimplified current terrain 50S. In this embodiment, the inclinationangle α is calculated from the simplified current terrain 50S and thetarget soil volume S, but the present invention is not limited to this.The inclination angle α may be calculated by sequential calculation fromthe horizontal plane 80, the current terrain 50, and the target soilvolume S.

In step S107, the estimated held soil volume S_(sum) is calculated. Theestimated held soil volume S_(sum) is an estimate of the soil volumeheld in the work implement 13 as a result of digging along the virtualsurface 70′ at the inclination angle α from the current position. Theestimated held soil volume S_(sum) is calculated on the basis of theestimated dug soil volume and current held soil volume. The virtualsurface 70′ is a virtual surface generated by the controller 26 andhaving the above-mentioned inclination angle α.

The estimated dug soil volume is an estimate of the soil volume dug upwhen the cutting edge of the work implement 13 is moved along thevirtual surface 70′ at the inclination angle α from the currentposition. More precisely, as shown in FIG. 7, the estimated dug soilvolume is the cross sectional area of the current terrain 50 locatedabove the virtual surface 70′ at the inclination angle α extending fromthe current position Zr (the surface area of the hatched portion in FIG.7).

The current position Zr may be the current cutting edge position P0. Or,it may be the position (Z0) of the current terrain 50 located in thevertical direction of the current cutting edge position P0.Alternatively, the current position Zr may be at the height Z_(GL) of aperpendicular from the current edge position P0 to a plane that includesthe bottom face of the crawler belt 16.

The current held soil volume is the volume of soil currently being heldby the work implement 13. The controller 26 calculates the current heldsoil volume on the basis of the difference between the current terrain50 and the trajectory of the cutting edge position P0, for example. Asshown in FIG. 8, the controller 26 calculates the cross sectional areaΔSc bounded by the height Z0′ of the current terrain 50 a specificlength of time Δt earlier, the height Z0 of the current terrain 50 atthe current position, the height Zc′ of the cutting edge position P0 aspecific length of time Δt earlier, and the height Zc of the currentedge position P0. The controller 26 then calculates the value obtainedby adding up the ΔSc value calculated at predetermined time intervalsΔt, as the current held soil volume. The controller 26 calculates thesum of the estimated dug soil volume and the current held soil volume asthe estimated held soil volume S_(sum).

The current held soil volume may be calculated from the traction forceof the work vehicle 1. For example, if the work vehicle 1 is equippedwith an HST, the traction force may be calculated from the hydraulicpressure supplied to the hydraulic motor of the HST, and the currentheld soil volume may be calculated from the calculated traction force.Alternatively, image information about the soil being carried by thework implement 13 may be acquired by a camera, and the controller 26 maycalculate the current held soil volume from the acquired imageinformation.

In step S108, it is determined whether or not a second startingcondition is satisfied. The second starting condition includes thefollowing condition (3).q1·S<S _(sum)  (3)

Here, symbol q1 is a predetermined constant. The symbol q1 is a valueless than 1. The symbol q1 is a value close to 1, such as a value ofabout 0.9. S is the above-mentioned target soil volume. Therefore, thecondition (3) means that the estimated held soil volume S_(sum) hasincreased from a value that is less than the target soil volume S, andhas reached a first held soil volume threshold (q1·S) determined fromthe target soil volume S.

When the second starting condition is satisfied, the flow proceeds tostep S109 shown in FIG. 9. When the second starting condition is notsatisfied, the flow returns to step S106. The processing from step S106to step S108 is repeated at predetermined intervals until the secondstarting condition is satisfied. While this processing is beingrepeated, the work vehicle 1 travels and moves. The virtual surface 70′is a plane extending obliquely from the work vehicle 1 in the traveldirection of the work vehicle 1. The virtual surface 70′ is set usingthe current position Zr as the base point. For example, the virtualsurface 70′ is set using the cutting edge position P0 at the distal endof the work implement 13 of the work vehicle 1 as a base point. Theposition or travel direction of the work vehicle 1 is changed by turningor travel of the work vehicle 1 until the second starting condition issatisfied by the virtual surface 70′ with the set inclination angle α.

In step S109, an inclined first virtual design surface 70 is produced.The first virtual design surface 70 is the virtual surface 70′ when thesecond starting condition is satisfied. Here, as shown in FIG. 10, thecontroller 26 produces a first virtual design surface 70 having aninclination angle α and extending from the current position Zr in thetravel direction of the work vehicle 1. However, if the inclined firstvirtual design surface 70 is equal to or greater than a maximum heightZ_(max), the controller 26 produces a first virtual design surface 70that extends horizontally at the maximum height Z_(max).

For the width direction of the work vehicle 1, the virtual designsurface shall be assumed to extend in the horizontal direction.Z_(offset) in FIG. 10 is a predetermined offset height. The offsetheight Z_(offset) may be zero.

In step S110, the work implement 13 is controlled along the firstvirtual design surface 70, which is the virtual surface 70′ when thesecond starting condition is satisfied. Here, the controller 26generates a command signal to the work implement 13 so that the cuttingedge position of the work implement 13 will move along the first virtualdesign surface 70 produced in step S109. The generated command signal isinputted to the control valve 27. Consequently, as the cutting edgeposition P0 of the work implement 13 moves along the first virtualdesign surface 70, digging work is performed on the current terrain 50.The movement of the work implement 13 along the first virtual designsurface 70 is started when the second starting condition is satisfied.Depending on the load borne by the work implement 13 and other sucheffects, the work implement 13 may not always be able to move asinstructed by the command signal, but to simplify the description, letus assume that the work implement 13 moves along the virtual designsurface 70 in response to the command signal.

In step S111 the held soil volume S_(held) is calculated. Here, thecontroller 26 calculates the held soil volume S_(held) in the samemanner as in the method for calculating the held soil volume givenabove.

In step S112, it is determined whether or not a first ending conditionis satisfied. The first ending condition includes that the held soilvolume S_(held) calculated in step S111 is greater than a predeterminedend determination threshold. The end determination threshold may be theabove-mentioned target soil volume S. Or, the end determinationthreshold may be determined from the above-mentioned target soil volumeS. When the first ending condition is satisfied, the flow proceeds tostep S113.

The first ending condition may include that the height Z0 of the currentterrain 50 at the current position has gone over a predetermined targetheight Z_(target). The target height Z_(target) is the height of thevirtual design surface 70 at the position where a value oft times theestimated held soil volume S_(sum) calculated in step S107 is firstexceeded when the estimated held soil volumes of the work implement 13are successively added up from the current position. Symbol t is apredetermined constant, and is a value less than 1. The symbol t is avalue close to 1, such as a value of about 0.95.

When the first ending condition is not satisfied the flow returns tostep S110. Until the first ending condition is satisfied, the processingfrom step S110 to step S112 is repeated at predetermined intervals.

In step S113, smoothing of the current terrain 50 is performed. The termsmoothing means processing to smooth out the height changes in thecurrent terrain 50. Here, the controller 26 smoothes the heights Z0 toZn at a plurality of points in current terrain 50 according to thefollowing formula (3).Z _(n_sm)=(Σ_(k=n−2) ^(n+2) Z _(k))/5  Formula 3

All the heights at a plurality of points of the current terrain 50 weresmoothed in this embodiment, but smoothing of the height Z0 of thecurrent terrain 50 at the current position may not be performed. In thatcase, for Z1, the average value for Z0, Z1, and Z2 is used as thesmoothed value of Z1. FIG. 11 shows the smoothed current terrain 50A. InFIG. 11, Z1_sm to Zn_sm indicate the heights of the smoothed currentterrain 50A.

In Formula 3, smoothing is performed with the average height at fivepoints, but the number of points used in the smoothing may be less thanfive, or may be greater than five. Also, what is calculated is notlimited to the average value of the height of the points to be smoothedand points ahead and behind, and may also be the average value of theheight of the points to be smoothed and points located in front.Alternatively, the average value of the height of the points to besmoothed and points located behind may be calculated. Or, some othersmoothing processing may be used, and not just the average value.

In step S114 a virtual design surface that follows along the currentterrain 50 is produced. Here, the controller 26 produces a secondvirtual design surface 71 along the smoothed current terrain 50A. Moreprecisely, as shown in FIG. 11, the controller 26 produces a secondvirtual design surface 71 in which the smoothed current terrain 50A hasbeen moved downward by a predetermined offset amount Z_(offset).However, the second virtual design surface 71 is set so as not to gobelow a final design terrain 60.

In step S115, the work implement 13 is controlled along the secondvirtual design surface 71. Here, the controller 26 generates a commandsignal to the work implement 13 so that the cutting edge position P0 ofthe work implement 13 will move along the second virtual design surface71 produced in step S114. The generated command signal is inputted tothe control valve 27. Consequently, the cutting edge position P0 of thework implement 13 moves along the second virtual design surface 71 tocarry out earthmoving work.

The above-mentioned offset amount Z_(offset) is set to press the bladeagainst the current terrain 50 during earthmoving work and decrease thesoil volume that leaks from the work implement 13. The offset amountZ_(offset) may be zero.

In step S116, it is determined whether or not a second ending conditionis satisfied. The second ending condition includes that the work vehicle1 has reversed by at least specific distance. When the second endingcondition is satisfied, the above-mentioned held soil volume S_(held) isreset, and the flow returns to step S101.

If the second ending condition has not been satisfied, the flow returnsto step S113. The processing from step S113 to step S116 is repeated atpredetermined intervals until the second ending condition is satisfied.

As described above, with the control system 3 for the work vehicle 1according to this embodiment, as shown in FIG. 12A, the controller 26determines whether or not there are undulations having a soil volumeequal to or greater than a predetermined undulation determinationthreshold S_(const) in the current terrain 50 ahead of the work vehicle1. If there are such undulations in front of the work vehicle 1, thatis, when the first starting condition is satisfied, the controller 26produces a virtual surface 70′ extending at an inclination angle α fromthe current position of the work vehicle 1. The inclination angle α ofthe virtual surface 70′ is less than the inclination angle θ of thecurrent terrain 50.

Next, FIG. 12B shows a state in which the work vehicle 1 has moved fromthe position in FIG. 12A to a position close to the current terrain 50.As shown in FIG. 12B, the controller 26 calculates the estimated heldsoil volume (the sum of the surface area of the hatched portion in FIG.12B and the current held soil volume) on the basis of the virtualsurface 70′. The controller 26 then determines whether or not theestimated held soil volume matches the target soil volume S. FIG. 12Cshows a state in which the work vehicle 1 has moved from the position inFIG. 12B to a position even closer to the current terrain 50. As shownin FIG. 12C, if the estimated held soil volume approximately matches thetarget soil volume S, that is, when the second starting condition issatisfied, the controller 26 recognizes the design surface 70′ as thefirst virtual design surface 70, and controls the work implement 13 sothat the work implement 13 will move along the inclined first virtualdesign surface 70. As a result, digging work is performed on the currentterrain 50.

FIG. 12 shows the current terrain 50 as a simplified contour. In FIGS.12A and 12C, the virtual (design) surface is depicted in uniquepositions with respect to the current terrain 50 in order to simplifythe drawings, but the position of the virtual (design) surfacecorresponding to the above description is not limited to these uniquelocations. For example, in FIG. 12C showing the start of the workoperation, the work implement 13 may be separated from the groundsurface.

Next, as shown in FIG. 13A, when the held soil volume S_(held) of thework implement 13 becomes greater than the target soil volume S, or whenthe height Z0 of the current terrain 50 at the current position hasreached the target height Z_(target), the controller 26 produces thesecond virtual design surface 71 that follows along the current terrain50. The controller 26 then controls the work implement 13 so that thework implement 13 will move along the second virtual design surface 71that follows the current terrain 50. Consequently, earthmoving work isperformed as shown in FIG. 13B.

When the work vehicle 1 reverses by at least a specific distance, theheld soil volume S_(held) of the work implement 13 is reset. Then, thework shown in FIGS. 12A to 12C and FIGS. 13A to 13B is repeated. Whenperforming repetitive tasks at the same work site, the work site terraininformation can be updated instantly with vehicle position informationfor the work vehicle 1 obtained from the position sensing device 31. Inthis case, the position sensing device 31 functions as a terraininformation acquisition device. The controller 26 updates the currentterrain 50 on the basis of the updated work site terrain information,and newly decides on the virtual design surfaces 70 and 71 based on theupdated current terrain 50. Consequently, the first virtual designsurface 70 is determined so that at a given work site (as shown in FIG.13C), the inclination angle α will gradually decrease. As a result, asshown in FIG. 13C, the inclination of the current terrain 50 graduallybecomes less steep, and digging is performed so as to approach the finaldesign terrain 60.

An embodiment of the present invention was described above, but thepresent invention is not limited to or by the above embodiment, andvarious modifications are possible without departing from the gist ofthe invention.

The work vehicle 1 is not limited to a bulldozer, and may be some othervehicle such as a wheel loader.

The work vehicle 1 may also be a vehicle that can be steered remotely.In that case, part of the control system 3 may be located outside of thework vehicle 1. For example, the controller 26 may be located outside ofthe work vehicle 1. The controller 26 may be disposed in a controlcenter that is away from the work site.

The operating device 25 may be disposed outside of the work vehicle 1.In that case, the cab may be omitted from the work vehicle 1.Alternatively, the operating device 25 may be omitted from the workvehicle 1. The work vehicle 1 may be operated by automatic control underthe controller 26 alone, without any input from the operating device 25.

The controller 26 may have a plurality of controllers separate from oneanother. For example, the controller 26 may include a remote controllerdisposed outside of the work vehicle 1 and an onboard controllerinstalled in the work vehicle 1. The remote controller and the onboardcontroller may be capable of communicating wirelessly. Some of thefunctions of the controller 26 discussed above may be executed by theremote controller, and the rest by the onboard controller. For example,processing for determining the virtual design surface may be executed bythe remote controller, and processing for outputting a command signal tothe work implement may be performed by the onboard controller.

In the above embodiment, the controller 26 produced the second virtualdesign surface 71 that followed along the current terrain 50 on thebasis of the smoothed current terrain 50A. However, the controller 26may produce the second virtual design surface 71 that follows thecurrent terrain 50 without any smoothing being performed.

In the above embodiment, a scenario of digging uphill was described, butdigging work under the same control as above may be performed for adownward slope as shown in FIG. 14A. In this case, the inclination angleα of the first virtual design surface 70 can be similarly calculatedusing Formula 2 given above.

With a downward inclination, the surface area that is hatched in FIG.14A may be calculated as the estimated dug soil volume discussed above.The held soil volume may be decided in the same way as the held soilvolume discussed above. As shown in FIG. 14B, the controller 26 maycontrol the work implement 13 so that the work implement 13 moves alongthe inclined virtual design surface 70 when the estimated held soilvolume S_(sum) that combines the estimated dug soil volume with the heldsoil volume approximately matches the target soil volume S. In thiscase, the second starting condition preferably includes the followingcondition (4).S _(sum) <q2·S  (4)

Symbol q2 is a predetermined constant. The symbol q2 is a value greaterthan 1. The symbol q2 is a value close to 1, such as a value of about1.1. Therefore, condition 4 means that the estimated held soil volumeS_(sum) has reached the second held soil volume threshold (q2·S)determined from the target soil volume S.

More specifically, condition 4 means that the estimated held soil volumeS_(sum) has decreased from a soil volume that exceeds the target soilvolume S, and has reached a value close to the target soil volume S (thesecond held soil volume threshold (q2·S)). The above-mentioned condition3 means that the estimated held soil volume S_(sum) has increased from asoil volume that is less than the target soil volume S, and has reacheda value close to the target soil volume S (the first held soil volumethreshold (q1·S)).

As shown in FIG. 14C, if the held soil volume S_(held) of the workimplement 13 is greater than the target soil volume S, or if the heightZ0 of the current terrain 50 at the current position has reached thetarget height Z_(target), the controller 26 may produce a second virtualdesign surface 71 that follows along the current terrain 50. Thecontroller 26 may then control the work implement 13 so that the cuttingedge position P0 of the work implement 13 moves along the second virtualdesign surface 71 that follows the current terrain 50.

The invention claimed is:
 1. A control system for a work vehicle, thesystem comprising: a current terrain acquisition device that acquirescurrent terrain information indicating a current terrain to be worked;and a controller configured to decide a virtual design surface locatedbelow the current terrain, the virtual design surface having aninclination angle, generate a command signal to a work implement of thework vehicle to move the work implement along the virtual designsurface, update the current terrain information with the current terrainacquisition device as movement proceeds, and modify the inclinationangle according to the updated current terrain information.
 2. Thecontrol system for a work vehicle according to claim 1, wherein thecontroller is further configured to decide the virtual design surface todecrease the inclination angle gradually, by repeatedly updating thecurrent terrain and deciding the virtual design surface.
 3. The controlsystem for a work vehicle according to claim 2, wherein the controlleris further configured to decide the inclination angle of the virtualdesign surface to be equal to or greater than a predetermined lowerlimit value.
 4. The control system for a work vehicle according to claim3, wherein the current terrain information includes height of thecurrent terrain from a current position of the work vehicle to a pointthat is a predetermined terrain recognition distance away, and thecontroller is further configured to decide the lower limit value fromthe terrain recognition distance and the height of the current terrain.5. The control system for a work vehicle according to claim 1, whereinthe virtual design surface extends at the inclination angle in a traveldirection of the work vehicle from a current position of the workvehicle.
 6. The control system for a work vehicle according to claim 1,wherein the controller is further configured to update the currentterrain when a predetermined ending condition is satisfied, and decidethe virtual design surface that is inclined at the inclination anglethat is smaller than the inclination angle of the updated currentterrain.
 7. The control system for a work vehicle according to claim 6,wherein the ending condition includes that the work vehicle travels inreverse over a distance equal to or greater than a specific distance. 8.A method for controlling a work vehicle, the method comprising:acquiring current terrain information indicating a current terrain to beworked; deciding an inclined virtual design surface located below thecurrent terrain; and generating a command signal to a work implement ofthe work vehicle to move the work implement along the virtual designsurface, the virtual design surface being decided so that an inclinationangle of the virtual design surface gradually decreases, by repeatedlyupdating the current terrain and deciding the virtual design surface. 9.A work vehicle comprising: a work implement; and a controller configuredto decide an inclined virtual design surface located below a currentterrain to be worked, move the work implement along the virtual designsurface, and decide the virtual design surface so that an inclinationangle of the virtual design surface gradually decreases, by repeatedlyupdating the current terrain and deciding the virtual design surface.10. The work vehicle according to claim 9, further comprising a positionsensing device that senses a position of the work vehicle and outputsposition information for the work vehicle to the controller, theupdating of the current terrain being performed with the positioninformation for the work vehicle.